1. Field of the Invention
This invention relates to a toner fixing unit employed in, for example, an electro-photographic printing apparatus. More specifically, this invention relates to a fixing unit in which a pressure roller, a sheet-separator and a cleaning wiper, each provided around a developer roller and all integrated in a single sub-frame, can be removed all together from the fixing roller by rotating the sub-frame.
2. Description of the Related Arts
Electro-photographic printing apparatus are typically composed as follows. A laser light modulated by data to be printed is scanned onto a photosensitive drum which has been charged with a high voltage so that a latent image is formed thereon. Developer containing toner is stirred in a toner tank and is electrostatically deposit on the latent image so as to develop a toner image thereon. Then, a sheet is fed on to the toner image so that the toner image is electrostatically transferred onto the sheet from the photosensitive drum. The sheet having the toner image thereon is then input to a fixing unit where the toner is pressed by a heat roller and a press roller to the sheet as well as heated so that the toner is melted thereon, i.e. fixed.
A typical prior art configuration of the fixing unit is schematically illustrated in FIG. 1. Heat roller (i.e. fixing roller) R1, press roller R2, separator 16a and cleaning wiper 17a are installed on a fixer unit frame 18a. On fixer unit frame 18a there are an inlet 90 and an outlet 91 through which sheet 12a having the toner image thereon is transported to and from rollers R1 and R2. Press roller R2 presses via a spring 81 sheet 12a towards the fixing roller R1 having heater lamp 80 therein. Separator 16a peels off sheet 12a from fixing roller R1. Cleaning wiper 17a typically formed of felt wipes off toner remaining on the surface of fixing roller R1.
Another typical prior art configuration is disclosed in Japanese Unexamined Patent Publication Sho 63-293576, where a pressure roller and a separator are installed on a sub-frame hinged onto a frame having fixing roller thereon so that they are removed together from the fixing roller.
It is very general in electro-photographic printing apparatus that the sheet is liable to go into between separator and fixing roller and furthermore between cleaning wiper and fixing roller, where the sheet is jammed, even though separator has been provided in order to remove the sheet from the fixing roller.
Problem of above-cited prior art configurations is in that the operation to remove the jammed sheet is troublesome and time-consuming, because if the sheet pinched under the separator and/or the cleaning wiper is forced to be pulled out the sheet is easily broken and may stay deep in the fixing unit. In removing the jammed sheet the separator is even likely to be broken. Moreover, the manual operation in the narrow space may cause the operator's fingers to get burnt.